1. Field of the Invention
The present invention relates to a flexible actuator that can be used for driving a robot capable of gripping, pinching, or pushing and a pet robot that acts like an animal.
2. Description of the Related Art
As described in Japanese Patent Laid-Open No. 5-172118 and Japanese Patent Laid-Open No. 5-164112, known actuators for gripping an object include a cylindrical elastic body having a plurality of pressure chambers therein and adjust a fluid pressure applied to each pressure chamber to curve and deform the cylindrical elastic body (hereinafter referred to as the first prior art).
Further, as described in Japanese Patent Laid-Open No. 2-17204, an actuator different from the first prior art is also known in which a driving source and a pump are integrated into a hydraulic cylinder (hereinafter referred to as the second prior art).
An actuator that operates as a robot finger of a robot must bend like a human finger, and enclose to grip a soft object such as a fruit or a paper cup, pinch a small object such as a screw with its tip, or bend to push a switch with its tip. In gripping the paper cup with the entire robot finger, a substantially even bending force is desirably produced throughout the finger. On the other hand, in pinching the object with the tip, a bending force proportional to a distance from the tip is desirably produced in terms of moment. Reducing the bending force at the tip saves power for bending.
However, in the first prior art, the actuator entirely bends with a predetermined curvature to grip the object, and do not have a structure in which an appropriate bending force is produced at each part. Thus, it is difficult to configure an actuator capable of performing various operations such as enclosing to grip the soft object, pinching the small object, or pushing the switch with the tip, with appropriate gripping forces like the human finger.
The second prior art is of the piston type, and requires many actuators and associated sensors or mechanisms to configure a flexible actuator, so that it is difficult to cause the actuator to operate as a robot finger.
Even if the actuators according to the first prior art and the second prior art are to be manufactured as pet robots that finely act like animals, many sensors and complex mechanisms must be provided to cause complex appearances.
Further, in the first prior art and the second prior art, an operating fluid must be supplied to the pressure chamber, or a pump that discharges the operating fluid from the pressure chamber must be placed outside via a fluid tube (referred to as an operating tube in the specification of the prior art) which cannot provide a small actuator. Thus, it is difficult to use the actuator as the pet robot that finely acts like an animal.
When a liquid is used as the operating fluid of the first prior art and the second prior art, a reservoir that stores the liquid is placed outside together with the pump. Between when the reservoir is above the pressure chamber (hereinafter referred to as a main liquid chamber) and when the reservoir is below the main liquid chamber, amounts of liquid supplied and discharged to and from the main liquid chamber by gravity change depending on changes in positions of the cylindrical elastic body. Thus, each change in the position of the cylindrical elastic body tends to cause a change in an amount of bending deformation.
The present invention has been achieved to solve the above described problems in the prior art, and has an object to provide a flexible actuator capable of gripping a soft object like a human finger and finely acting like an animal, and also avoiding a change in an amount of liquid moving between a reservoir and a main liquid chamber by gravity even if a liquid is used as an operating fluid, and keeping a constant amount of bending deformation even if the actuator changes its position.
To solve the problems, a flexible actuator according to the invention has the following configuration. Specifically, the flexible actuator according to the invention includes: a long movable part that is bent by a liquid moving toward a main liquid chamber; a reservoir where the liquid moves to and from the main liquid chamber; a pump that moves the liquid between the reservoir and the main liquid chamber; and a pump driving unit that controls the pump, wherein the movable part includes a long tube that forms the main liquid chamber, a plurality of frame members aligned at predetermined intervals along a length of the tube, and a resilient core member that holds the alignment of the frame members, the tube is made of a flexible elastic material, and includes a plurality of flat expanded hollow portions provided at predetermined intervals along the length and a narrow hollow portion that communicates between the expanded hollow portions, the plurality of frame members are formed by flat members and longitudinally hold the plurality of expanded hollow portions by the narrow hollow portion of the tube inserted into recesses or holes provided on sides abutting the core member, the movable part has a first bending portion that produces a large bending force and a second bending portion that produces a small bending force, the expanded hollow portion placed in the first bending portion has a large transverse cross sectional area, and the expanded hollow portion placed in the second bending portion has a small transverse cross sectional area.
According to the invention, the expanded hollow portion placed in the first bending portion has the large transverse cross sectional area, and the expanded hollow portion placed in the second bending portion has the small transverse cross sectional area, so that the first bending portion produces the large bending force and the second bending portion produces the small bending force simply by a fluid flowing into the tube to increase capacities of the expanded hollow portions, thus allowing operations different from those of a conventional actuator.
The flexible actuator may be used as a robot finger or the like, and the expanded hollow portion at a base of the movable part as the first bending portion may have a largest transverse cross sectional area, with transverse cross sectional areas of the expanded hollow portions gradually decreasing toward a tip of the movable part, and the expanded hollow portion at the tip of the movable part as the second bending portion may have a smallest transverse cross sectional area.
When the flexible actuator with such a configuration is used as the robot finger, the base of the movable part that is a root of the robot finger produces a large bending force, and the tip of the movable part that is a tip of the robot finger produces a small bending force to bend. This allows the actuator to reliably enclose to grip a soft object, pinch a small object, or push a switch with the tip, and act like a human finger.
The transverse cross sectional area of the expanded hollow portion placed in the second bending portion may be 30% to 80% of the transverse cross sectional area of the expanded hollow portion placed in the first bending portion.
In this way, providing the second bending portion at the base prevents a large force to fold the base from being applied in gripping the object, thus allowing the object to be properly gripped. Further, an average sectional area at the tip that requires no large bending force is small, thus a total amount of hydraulic fluid required for bending decreases to allow quick bending and extension.
The core member may be a member having gradually decreasing resilience from the base toward the tip of the movable part. Alternatively, the core member may be a tapered plate material in which a base has a large width, with widths gradually decreasing toward a tip, and the tip has a smallest width.
This exerts no influence on bending displacement of the movable part. When the movable part bends under a no-load or light-load condition, the core member having the large width at the base prevents the bending force from concentrating on the base of the movable part, thus allowing the entire movable part to bend with an even curvature.
The flexible actuator may be used as an actuator for massaging a shoulder, and the expanded hollow portion at a center along the length of the movable part as the first bending portion has a largest transverse cross sectional area, with transverse cross sectional areas of the expanded hollow portions gradually decreasing toward both ends along the length of the movable part, and the expanded hollow portions at the both ends of the movable part as the second bending portion have a smallest transverse cross sectional area.
When the flexible actuator with such a configuration is used as the actuator for massaging a shoulder by being applied to a human shoulder, a bending force of the expanded hollow portion at the center along the length increases to ensure massaging the shoulder.
The transverse cross sectional area of the expanded hollow portion placed in the second bending portion may be approximately 60% of the transverse cross sectional area of the expanded hollow portion placed in the first bending portion.
In this way, the bending force of the first bending portion that requires a large bending force in operation such as pinching increases and concentrates since the second bending portion requires a small bending force and a reduced amount of hydraulic fluid, thus providing quick shoulder massage.
The core member may be a member having gradually decreasing resilience from the center along the length toward the both ends of the movable part. Alternatively, the core member may be a plate material in which a center along a length has a large width, with widths gradually decreasing toward both ends, and the both ends have a smallest width.
In this way, the core member has low resilience at a portion where the moving part produces a small bending force. Thus, there can be provided an actuator for massaging a shoulder capable of enclosing the entire shoulder for massaging with a constant curvature in massaging with a small force.
There may be provided a flexible actuator including: a long movable part that is bent by a liquid moving toward a main liquid chamber; a reservoir where the liquid moves to and from the main liquid chamber; a pump that moves the liquid between the reservoir and the main liquid chamber; and a pump driving unit that controls the pump, wherein the movable part includes the main liquid chamber and the reservoir placed along a length, a plurality of frame members aligned at predetermined intervals along lengths of the main liquid chamber and the reservoir, and a resilient core member that holds the alignment of the frame members. The main liquid chamber and the reservoir are placed along a length in the movable part, so that even if a position of the movable part changes, an amount of fluid supplied from the reservoir to the main liquid chamber, and an amount of fluid discharged from the main liquid chamber to the reservoir by gravity do not change. Therefore, the change in the position of the movable part causes no change in an amount of bending deformation of the pump driving unit. The main liquid chamber and the reservoir are placed along the length to provide a small actuator.
The reservoir may be formed by a tube made of an expandable and shrinkable elastic material, and includes a plurality of flat expanded hollow portions provided at predetermined intervals along the length, and a narrow hollow portion that communicates between the expanded hollow portions.
This allows a plurality of reservoirs to be connected by a tube to configure one reservoir with a large capacity and a simple structure, thus providing an inexpensive actuator.
The main liquid chamber may be formed by a tube made of an expandable and shrinkable elastic material, and includes a plurality of flat expanded hollow portions provided at predetermined intervals along the length, and a narrow hollow portion that communicates between the expanded hollow portions, and each expanded hollow portion of the main liquid chamber may be placed to longitudinally overlap each expanded hollow portion of the reservoir. This provides a smaller actuator.
The plurality of frame members may be hollow members with cavities therein, and the expanded hollow portions of the reservoir may be placed in the cavities of the plurality of frame members.
This provides a small actuator with a short length. Each expanded hollow portion of the reservoir is placed in each cavity of the frame members, thus the fluid stored in the expanded hollow portions of the reservoir is not influenced by pressure due to bending of the movable part.
The tube that forms the reservoir may be made of a flexible elastic material such that each expanded hollow portion of the tube can expand into the entire cavity.
This allows a space in the cavity of the frame member to be effectively used as the reservoir, thus providing a small actuator.
The plurality of frame members may include air holes that communicate between the cavities and an outside.
This allows the air in the cavity to pass through the air hole to the outside when the expanded hollow portion of the tube that forms the reservoir expands into the cavity of the frame member. Thus, the air in the cavity exerts no influence on expansion of the expanded hollow portion of the tube that forms the reservoir.
The pump may be built in an actuator body integral with an end of the movable part. In this case, the pump is built in the actuator body to be compact, thus the actuator can be used as a pet robot with a simple appearance.
A sensor that detects the amount of moving fluid may be placed in any of the pump, the main liquid chamber, or the reservoir, and the pump driving unit may control the pump based on information from the sensor.
This allows control of the movable part with high accuracy, and for example, causes fine acting like an animal when the actuator is used as the pet robot.
There may be provided a flexible actuator including: a plurality of flat expanded hollow portions made of a flexible elastic material and provided at predetermined intervals along a length; a long tube in which a liquid chamber is formed by a connection tube that communicates between the plurality of expanded hollow portions and extends along the length; a plurality of flat frame members that longitudinally hold the plurality of expanded hollow portions of the tube with surface contact; and a connection that holds the adjacent frame members so as to swing against each other, wherein the actuator further includes at least one spring member for recovering rotating angle between the frame members, and the spring member is placed to produce a spring force in a compressing direction of the expanded hollow portions of the tube by the adjacent frame members.
In this case, the actuator includes at least one spring member for recovering the rotating angle between the frame members, so that the spring member produces the spring force in the compressing direction of the plurality of expanded hollow portions to return the fluid from the tube, thus recovering to an upright condition. Further, the spring member is independent, thus facilitating adjusting the resilience to minimize repulsion in large bending due to the resilience.
There may be provided a flexible actuator including: a first actuator that bends in a predetermined direction; and a second actuator joined to a base of the first actuator, wherein the first actuator includes: a plurality of flat expanded hollow portions made of a flexible elastic material and provided at predetermined intervals along a length; a long tube in which a liquid chamber is formed by a connection tube that communicates between the plurality of expanded hollow portions and extends along the length; a plurality of flat frame members that longitudinally hold the plurality of expanded hollow portions of the tube with surface contact; and a connection that holds the adjacent frame members so as to swing against each other, and the second actuator is placed between the frame member at the base of the first actuator and an actuator mounting portion, and the entire first actuator is slanted in a direction different from a bending direction of the first actuator.
In this way, the first actuator that bends in a predetermined direction, and the second actuator that slants the entire first actuator in the direction different from the bending direction of the first actuator are provided, thus allowing a position of a tip frame member corresponding to the finger tip to be changed when the actuator is used as a robot finger of a robot to precisely grip a small object.
The first actuator may include at least one spring member for recovering rotating angle between the frame members, and the spring member may be placed to produce a spring force in a compressing direction of the expanded hollow portions of the tube by the adjacent frame members. In this case, the spring member produces the spring force in the compressing direction of the plurality of expanded hollow portion to return the fluid from the tube, thus recovering to the upright position. Further, the spring member of the first actuator is independent, thus facilitating adjusting the resilience to minimize repulsion in large bending due to the resilience.
Further, ends of the spring member may be secured to both ends of the aligned frame members. Thus, even in a local and deep bending condition, the spring member does not locally and excessively extend to increase durability.
Each of the frame members may include a guide that guides extension and shrinkage of the spring member. This prevents the spring member from being shifted in bending the flexible actuator.
The frame members and the connection may be integrally molded of resin. This provides a flexible actuator that includes a small number of components, has a reduced weight, and is easy to assemble.